This invention relates to a blend of (1) a linear copolymer that contains both carbonate and carboxylate moieties and (2) an aromatic polycarbonate resin.
Polycarbonate resins are widely employed in applications where a tough, rigid thermoplastic is required. Of particular importance are polycarbonates derived from bisphenol-A diols as are described in U.S. Pat. No. 3,028,365. However, the usefulness of polycarbonates is limited by the precipitous decline in impact strength where the resin is present in greater than a certain thickness (so-called "thickness sensitivity") as well as the relatively poor low-temperature toughness and the moderate heat distortion temperature of the resin.
U.S. Pat. No. 3,792,115 describes blends of a polycarbonate with a polyarylene ester. These blends are reported to possess improved impact strength and heat deformation resistance.
Linear copolymers containing ester and carbonate groups having improved thermal properties relative to polycarbonates have recently been introduced. U.S. Pat. Nos. 4,156,069 and 4,105,633 describe polyestercarbonate copolymers containing alternating ester and carbonate groups. These alternating copolymers are disclosed to possess improved impact and thermal properties compared with a typical polycarbonate resin. U.S. patent application Ser. No. 200,759, filed Oct. 27, 1980, now U.S. Pat. No. 4,330,662, describes polyestercarbonates consisting of repeating units corresponding to the formula ##STR1## wherein R is an aromatic hydrocarbylene moiety, R' is a meta or para phenylene group and x is a number from 0.05 to 10. This copolymer possesses good processability and low temperature toughness.
The mechanical and thermal properties of all of the aforementioned polyestercarbonate copolymers exhibit considerable variance dependent on the ratio of ester to carbonate moieties present. Heretofore, it has been necessary to tailor the copolymer composition to provide the desired balance of properties. The manufacture of the copolymers in the relatively small quantities for specific applications has significantly increased the cost of the resin relative to the projected cost of larger scale operations. It would therefore be desirable to produce an engineering plastic the properties of which can be more economically varied to meet the requirements of a variety of end uses.